I/O INTERFACING
1. What is
memory mapped I/O?
This is
one of the techniques for interfacing I/O devices with μp. In memory mapped
I/O, the I/O devices assigned and identified by 16-bit addresses. To transfer
the data between MPU and I/O devices memory related instructions ( such as LDA,
STA etc.) and memory control signals ( MEMR, MEMW) are used.
2. What is I/O mapped I/O?
This is
one of the techniques for interfacing I/O devices with μp. In I/O mapped I/O,
the I/O devices assigned and identified by 8-bit addresses. To transfer the data
between MPU and I/O devices I/O related instructions ( IN and OUT ) and I/O
control signals (IOR, IOW) are used.
3. What
is simplex and duplex transmission?
Simplex
transmission: data are transmitted in only one direction. Duplex transmission:
data flow in both directions. If the transmission goes one way at a time, it is
called half duplex; if it goes both way simultaneously, then it is called full
duplex
4. Define
Baud.
The rate
at which the bits are transmitted, bits per second is called Baud.
5. What are
the signals available for serial communication? SID – serial input data
SOD –
serial output data
6. What is
USART?
It is a
programmable device. Its function and specification for serial I/O can be
determined by writing instructions in its internal registers. The Intel 8251A
USART is a device widely used in serial I/O.
7. Write
the features of 8255A.
The 8255A
has 24 I/O pins that can be primarily grouped primarily in two 8-bit Parallel
ports: A and B, with eight bits as port C. The 8-bits of port C can be used as
two 4-bit ports:C UPPER CU and CLOWER CL.
8. What
is BSR mode?
All
functions of 8255 are classified according to 2 modes. In the control word, if
D7 = 0, then it represents bit set reset mode operation. The BSR mode is used
to set or reset the bits in port C.
9. What
is mode 0 operation of 8255?
In this
mode, ports A and B are used as two simple 8-bit I/O ports and port C as two
4-bit ports. Each port can be programmed to function as an input port or an
output port. The input/ output features in mode 0 as follows:
i. outputs are latched
ii. inputs are not latched
iii. ports do not have handshake or interrupt
capability.
10. What
are the modes of operation supported by 8255?
i. Bit set reset mode(BSR)
ii. I/O
mode Mode 0 Mode1 Mode2
11. Write
the control word format for BSR mode.
12. What
is ADC and DAC?
The
electronic circuit that translates an analog signal into a digital signal is
called analog-to-digital converter(ADC).
The
electronic circuit translates a digital signal into an analog signal is called
Digital-to-analog converter(DAC).
13.
Define conversion time.
It is
defined as the total time required to convert an analog signal into a digital
output. It is determined the conversion technique used and by the propagation
delay in various circuits.
14.
What are the functions to be performed by μp while
interfacing an ADC?
i. Send a
pulse to the START pin.
ii. Wait
until the end of conversion
iii. Read the
digital signal at an input port
15.
Write the different types of ADC.
i. Single
slope ADC
ii. Dual
slope ADC
iii. Successive
approximation ADC
iv.Parallel
comparator type ADC
v. Counter
type ADC
16.
What is resolution time in ADC?
It is
defined as a ratio of change in value of input voltage Vi, needed to change the
digital output by 1 LSB. If the full scale input voltage required to cause a
digital output of all 1‟s is ViFS. Then the resolution can be
given as
Resolution
= ViFS / (2n-1)
17. List the
functions performed by 8279.
i. It has
built-in hardware to provide key debounce.
ii. It
provides a scanned interface to a 64 contact key matrix.
iii. It
provides multiplexed display interface with blanking and inhibit options.
iv. It
provides three input modes for keyboard interface.
18.
What is key debounce?
The push
button keys when pressed, bounces a few times, closing and opening the contacts
before providing a steady reading. So reading taken during bouncing may be
faulty. Therefore the microprocessor must wait until the key reach to steady
state. This is known as key debounce.
19.
What are the operating modes in 8279? i. Scanned
keyboard mode
ii.
Scanned sensor matrix iii. Strobed input
20.
What is N-key rollover?
In N-key
rollover each key depression is treated independently from all others. When a
key is depressed, the debounce logic is set and 8279 checks for key depress
during next two scans.
21.
Find the program clock command word if external
clock frequency is 2 MHz. Prescalar value = (2 x106) / (100 x 103) = (10100)2
Therefore
command word = (00110100)2
22.
What is multiple interrupt processing capability?
Whenever
a number of devices interrupt a CPU at a time, and id the processor is able to
handle them properly, it is said to have multiple interrupt processing
capability
23. What
is hardware interrupt?
An 8086
interrupt can come from any one of three sources. One sources is an external
signal applied to the nonmarkable interrupt(NMI) input in or to the interrupt
(INTR) input pin. An interrupt caused by the signal applied to one of these
input is referred to as a hardware interrupt.
24. What
is software interrupt?
The
interrupt caused due to execution of interrupt instruction is called software
interrupt.
25. What
are the two types of interrupts in 8086? The two types of interrupts are:
i.
External interrupts:
In this,
the interrupt is generated outside the processor. Example: Keyboard interrupt.
ii.
Internal interrupts:
It is
generated internally by the processor circuit or by the execution of an
interrupt instruction. Example: Zero interrupt, overflow interrupt.
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